1. Field of the Invention
The present invention relates to compositions and methods for metal substrate treatment. More particularly, the present invention relates to compositions comprising epoxy-novolac resins containing a side chain substituent, and methods for treatment of metal and polymeric substrates using these compositions. These methods provide improved corrosion resistance and/or paint adhesion properties to the substrate being treated.
2. Background Information
The present invention is directed to methods which are generally useful in the art of metal substrate treatment, particularly the treatment of phosphatized metal substrates, and more particularly the post-treatment of phosphatized metal substrates. Such treatment imparts improved corrosion resistance to the substrate, and improves the adhesion of final coating layers such as paints, inks, lacquers and plastics. The need for applying protective coatings to metal substrates for improved corrosion resistance and/or paint adhesion characteristics is well known in the art of metal finishing, as well as other metal arts. The usual technique for applying such protective coatings to metal substrates involves contacting a clean metal substrate with a solution containing phosphate and possibly other metal ions to form a corrosion resistant, nonreactive phosphate complex coating on the metal substrate. Because such coatings convert the metal substrate from a chemically active surface readily susceptible to oxidation to one having improved corrosion resistance and/or paint adhesion properties, they are known in the art as "conversion coatings."
The corrosion resistance and paint adhesion of conversion coatings can be further enhanced by treating the metal substrate with a post-treatment solution. Typical of such solutions are dilute aqueous acidic solutions containing a hexavalent chromium compound. Because of the toxic nature of hexavalent chromium compounds, however, expensive treatments must be used to remove chromates from effluent water to prevent the pollution of rivers, streams, drinking water sources, and the like. Therefore, although chromium post-treatment solutions and processes are known to be effective, recent development efforts have been directed to discovering alternatives to chromium-containing compounds for post-treatment of conversion coatings.
U.S. Pat. No. 4,376,000 discloses processes for post-treating a phosphate-type conversion coated metal surface comprising contacting the surface with polyvinylphenol or its derivatives. U.S. Pat. Nos. 4,433,015 and 4,517,028 disclose aqueous compositions comprising polyvinylphenol and polyalkenylphenol derivatives and acid salts thereof, respectively; processes for treating a metal surface comprising contacting said surface with these aqueous compositions are also disclosed. U.S. Pat. No. 4,457,790 claims an aqueous solution comprising a metal ion and a polyvinylphenol derivative or acid salt thereof. A process for treating a metal surface comprising contacting said surface with the aqueous solution is also disclosed.
U.S. Pat. No. 5,523,363 relates to a resin obtained by reacting an epoxy resin, an amino compound and a phenol compound, and an epoxidized novolac-substituted phenolic resin. The resin is useful as an aqueous coating, particularly for cationic electrocoatings. There is no teaching of polymerizing the components, of using Mannich derivatives, or modifying an epoxy-novolac resin by adding a Mannich-derivatized bisphenol thereto, or of using the resin to treat metal or polymeric surfaces.
U.S. Pat. Nos. 5,039,310 and 4,883,826 disclose phenol-containing Mannich bases useful in lubricants, surfactants and dispersants. U.S. Pat. No. 5,039,310 discloses the reaction product of a Mannich-derivatized alkali metal salt of a phenol or C.sub.1 -C.sub.16 alkylphenol and a C.sub.2 -C.sub.3 alkylene epoxide. U.S. Pat. No. 4,883,826 discloses Mannich polyols prepared from the reaction between a phenolic compound, formaldehyde and a mixture of diethanolamine and at least one other alkanol amine. Again, neither patent teaches the addition to an epoxy-novolac resin of a Mannich derivative of a bisphenol to form a resin useful in the treatment of metals or polymeric substrates.
U.S. Pat. No. 5,298,289 discloses processes for treating certain plastic or painted surfaces with liquid surface treatment comprising water and a water soluble or dispersible polymer which contains substituted aminomethyl groups on some of the novolac phenyl rings in the backbone of the polymer. Other polymer compounds useful in metal treatment are disclosed in U.S. Pat. Nos. 5,116,912, 5,039,770 and 5,266,410 and EP 0 319 016. One significant difference between these compounds and those of the present invention is that the Mannich derivative is on the backbone of the phenol ring, rather than being attached as a side chain on the epoxy portion of the resin.
U.S. Pat. No. 5,324,347 relates to a composition comprising a liquid solvent or dispersant or surface coating composition and a 2,6-bis(substituted aminomethyl)phenol. There is no teaching that the phenol be polymerized with or otherwise reacted with an epoxy-novolac resin.
U.S. Pat. Nos. 5,389,405, 5,412,011 and 5,451,431 disclose aqueous solutions for coating a metal surface comprising a polymer, a silicate and an organofunctional silane. Methods of coating a metal surface comprising contacting said surface with the aqueous solutions are also disclosed.
U.S. Pat. No. 4,917,729 discloses metal chelating compounds that are Mannich derivatized bisphenol compounds having two Mannich groups, one attached to each ring of the bisphenol A. The compositions are stated as being useful for corrosion inhibition and adhesion promoting on a metal substrate. The patent does not appear to disclose addition of the Mannich derivatized bisphenol A to an epoxy-novolac resin.
U.S. Pat. Nos. 4,795,505 and 4,792,335 relate to compounds having only a single phenol ring and a single Mannich substituent and methods for inhibiting corrosion of metal substrates using these compounds.
WO 93/09265 discloses a treatment for the formation of a corrosion resistant film on metal surfaces. This treatment includes use of a phosphate surface-treatment bath containing a cationic organic polymeric compound having at least one cationic nitrogen atom. Disclosed as one of the polymeric compounds is the adduct of HN(CH.sub.3).sub.2 with a bisphenol A epoxy resin.
WO 95/28449 discloses a polymer composition and method for using the composition in the treatment of metal surfaces. The polymer is a Mannich derivative of a novolac resin. The disclosure does not appear to teach an epoxy form of the novolac resin, or addition of a derivatized bisphenol resin to an epoxy-novolac resin.
European Patent Application 639,627 discloses aqueous solutions for pre-treating a metal surface, particularly aluminum, consisting essentially of an anionic polyacrylamide copolymer. A method of coating a metal surface which comprises contacting said surface with any of the aqueous solutions is also disclosed. Uses of other acrylate-containing compositions in treating aluminum are disclosed in U.S. Pat. Nos. 4,191,596 and 5,122,202.
Mannich condensates of a substituted phenol and an alkylamine containing internal alkoxy groups are disclosed in European Patent Application 469,203.
There remains a very real and substantial need for chrome-free methods for treating various metal substrates, particularly phosphatized metal surfaces. The present invention addresses this need.